1. Field of the Invention
This invention relates to a lightweight exhaust-gas manifold and exhaust-gas pipe ducting for internal combustion gasoline- and diesel-fueled engines, and more specifically to improved structures for an exhaust-gas manifold and exhaust-gas pipe ducting which are fabricated from carbon-carbon composite materials.
2. Description of the Related Art
Conventional internal combustion gasoline- and diesel-fueled engines employ exhaust-gas manifolds and ducting fabricated from cast iron, steel, or iron with ceramic liners. These manifolds are well known to the art to be heavy and thermally conductive, and to lose strength at elevated engine operating temperatures, i.e., above 600 degrees Fahrenheit. The weight of an exhaust-gas manifold adds considerably to the total engine weight of an aluminum block automobile engine. Hence, reducing the weight of an exhaust-gas manifold and ducting would have a dramatic effect on total engine weight. On the other hand, in large industrial diesel engine applications, in which the weight of an exhaust-gas manifold and ducting is minimal with respect to the total engine weight, the excess weight is less of a concern.
The high thermal conductivity and high specific heat of cast-iron and steel exhaust manifolds and exhaust ducting result in considerable "through-the-wall" heat loss into the environment. While automobile engine manufacturers often utilize this heat loss to preheat air for cold-starting purposes, for the most part, "through-the-wall" heat loss reduces engine operating efficiency. In internal combustion engines equipped with a turbocharger, heat loss between the exhaust valves and the turbocharger reduces the energy level of the working gas driving the turbocharger compressor, which results in reduced performance of the turbocharger. In internal combustion engines with a catalytic converter, electric heaters, or burners, must be installed upstream of the converter to compensate for the heat loss, to ensure "light-off" of the converter during the warm-up phase of engine operation.